Diesel engines may be classified broadly as slow speed, medium speed and high speed engines. Slow speed engines typically are two-stroke cycle engines operating in the range of about 57 to 250 rpm. Medium speed engines may be two-stroke or four-stroke cycle engines operating in the range of 250 to 110 rpm. High speed engines may be two stroke or four-stroke engines operating in the range of 1100 to 3000 rpm.
Slow-speed and medium-speed diesel engines usually run on residual fuels containing high levels of sulfur, for example, in the range of about 0.5 wt % to 5 wt % which can cause corrosive wear necessitating costly engine overhauls. High speed engines usually run on distillate fuels which also contain sulfur albeit somewhat lower levels than residual fuels. Lubricant formulators therefore use various additives to reduce such wear and enhance engine performance. Thus, metallic detergents are used in diesel oil lubricants to maintain engine cleanliness; and antioxidants are used to extend the lubricant's useful life. Various other additives may be employed in preparing a fully formulated oil. These include such things as anti-foamants, pour point depressants and the like.
The art of lubricating oil formulation, of course, has become increasingly complex not only because the performance requirements sought by engine manufacturers and users are becoming more stringent but because, as is known in the art, use of one type of additive in a lubricant composition can have a negative impact on the function of another type of additive in that composition. Consequently, there is always a need for improved lubricant compositions which need typically is met by extensive research.
The present invention has as an objective meeting the need for to improved diesel engine lubricating compositions.
Another object of the invention is to provide a lubricating composition that reduces corrosion and wear in diesel engines.
Yet another object of the invention is to provide lubricating compositions suitable for use in diesel engines operating on high sulfur fuels.